1. Field of the Invention
The present invention relates to a magnetooptical recording apparatus that records information on a magnetooptical disk, and more particularly to an improvement in a magnetic head that slides on the magnetooptical disk.
2. Related Background Art
Up to now, there has been known a magnetooptical disk recording/playback apparatus that records or plays back information with respect to a magnetooptical disk having a magnetooptical recording layer which is formed of a vertically magnetized film as a recording medium. The recording system of the magnetooptical disk recording/playback apparatus is roughly classified into a magnetic field modulation system and a light modulation system. Of those systems, in the magnetic field modulation system, an orientation of an external magnetic field is reversed in accordance with information to be recorded while irradiating a laser beam having a desired intensity, to thereby record information.
In recent years, this magnetic field modulation system is applied to a portable product such as an MD (mini disk) or a digital disk cam coder (movie) device as an over-write recording system, that is, a recording system that is rewritable directly without an erasing process.
In the magnetic field modulation system, a magnetic field is applied the optical axis of a light spot that is irradiated from an objective lens of an optical pickup which opposes a magnetic head through the magnetooptical disk arranged therebetween. Therefore, when recording/playback operation is conducted on the disk received in a cartridge as in the MD, there is required a mechanism that opens a shutter of the cartridge and moves up and down the magnetic head with respect to a disk recording surface. The ascending and descending operation, that is, the vertical movement from the disk recording surface that is received in the cartridge by an amount corresponding to the thickness of the cartridge is required for the magnetic head. The amount of the vertical movement thus required is a factor that limits thickness reduction of the apparatus and the like, and a height of from a movable support point of the magnetic head to the magnetooptical disk recording surface and a length of the magnetic head support portion adversely affect the disk surface deflection as a displacement in the tangential direction.
Hereinafter, a conventional magnetooptical playback apparatus employing the magnetic field modulation system will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view showing a state in which a magnetic head 37 is in contact with a magnetooptical disk 1 which is received in a cartridge 2, and FIG. 2 is a cross-sectional view showing a state in which the cartridge 2 is discharged. In the conventional apparatus, a magnetic head movable arm 31 is rotatably supported about a rotating portion 30a of a support arm 30 as a center. At the leading portion of the magnetic head movable arm 31, the magnetic head 37 comes into contact with the magnetooptical disk 1 with a constant pressure by means of a leaf spring 32.
In this example, as shown in FIG. 1, in a recording operation, the magnetic head movable arm 31 is rotated about the rotating portion 30a as a center by a drive means (not shown) and is brought into contact with the magnetooptical disk 1 with a constant pressure. On the other hand, as shown in FIG. 2, in the discharge operation of the cartridge 2, the magnetic head movable arm 31 rotates clockwise about the rotating portion 30a as a center so that the magnetic head 37 is escaped upward. Also, when the cartridge 2 is loaded within the apparatus, the magnetooptical disk is positioned by a magnet chucking means using a turntable and rotates at a desired rotating speed. In this example, the magnetic head 37 and the optical pickup are so disposed as to oppose each other through the magnetooptical disk 1 arranged therebetween. The magnetic head 37 and the optical pickup are adjusted in position so that the optical axis of the light beam which is irradiated from the objective lens is made to coincide with the intensity center of a magnetic field which is applied from the magnetic head 37, and thereafter fixed to each other by a screw.
The magnetic pole core of the magnetic head 37 used in the magnetic field modulation system is generally made of Mn—Zn ferrite and relatively low in magnetic permeability. Therefore, in order to generate a magnetic field sufficient to conduct direct over-write, a large current needs to flow in a coil which is wound on the magnetic pole core. Also, with regard to the magnetic pole of the magnetic head 37, the recent trend is to reduce the sectional area of the magnetic field generation surface so as to allow adaptation to high-frequency recording, and to reduce an inductance in order to reverse the magnetic field at a high frequency of several tens MHz. It is important to make the center of the magnetic field intensity of the small magnetic head 37 and the center of the light spot from the optical pickup 2 coincide with each other with high precision to perform a recording and playback operation in a satisfactory manner.
However, in the above-mentioned conventional recording apparatus, in the case where the surface deflection, eccentricity or the like occurs in the magnetooptical disk 1, the center of the irradiation beam from the optical pickup and the magnetic pole core of the magnetic head 37 are displaced with respect to each other in the radial direction and in the tangential direction. In the case of radial displacement, that is, the disk eccentricity, since the magnetic pole core size is determined taking into account a standard prescribed amount of disk eccentricity, the core size depends on the amount of eccentricity. However, regarding the amount of eccentricity in the tangential direction, the cross-sectional area of the core configuration must be made as small as possible in consideration of high-frequency recording, so that the core size becomes necessarily small. For that reason, when the disk surface deflection or the like occurs, it is impossible to obtain a favorable positional relationship between the light spot and the magnetic field generation region which is generated from the magnetic pole core of the magnetic head 37, particularly in the tangential direction.
Under the above-mentioned circumstances, in the conventional suspension structure, in consideration of a height arrangement that would prevent the collision of the magnetooptical disk 1 with the magnetic head 37 when loading and unloading the magnetooptical disk 1, the magnetic head 37 is rotated with a desired position as the movable fulcrum 30a of the magnetic head. In this structure, an angle formed by a straight line that connects the center point of the magnetic head 37 and the rotating point 30a with respect to the disk surface becomes large. When the angle is large, the magnetic head 37 is largely displaced in the tangential direction due to the occurrence of the disk surface deflection, that is, the variation in the height of the disk.
FIG. 3 is a view showing a state in which the magnetic head is displaced in the tangential direction due to the disk surface deflection. It is apparent that the amount of displacement becomes larger in proportion to a distance of from the rotating portion 30a of the magnetic head movable arm 31 to the magnetooptical disk surface. Therefore, the height distance must be made as small as possible, but in the conventional structure, because the magnetic head is so structured as to be supported by the movable arm, the height of the arm is required to some degree and thus the displacement of the magnetic head in the tangential direction cannot be avoided.
On the other hand, in recent years, reduction in the diameter of the optical disk has advanced, and there is a trend toward increased information recording density per square inches. Moreover, the size of the magnetic pole core of the magnetic head 37 is made increasingly smaller. Taking the above situation into consideration, it is desirable to reduce not only the displacement in the radial direction but particularly in the tangential direction.